Entries linking to catholicity
mid-14c., "of the doctrines of the ancient Church" (before the East/West schism), literally "universally accepted," from French catholique, from Church Latin catholicus "universal, general," from Greek katholikos, from phrase kath' holou "on the whole, in general," from kata "about" + genitive of holos "whole" (from PIE root *sol- "whole, well-kept").
Medieval Latin catholicus was practically synonymous with Christian and meant "constituting or conforming to the church, its faith and organization" (as opposed to local sects or heresies). With capital C-, applied by Protestants to the Church in Rome c. 1554, after the Reformation began. General sense of "embracing all, universal" in English is from 1550s. Meaning "not narrow-minded or bigoted" is from 1580s. The Latin word was rendered in Old English as eallgeleaflic.
word-forming element making abstract nouns from adjectives and meaning "condition or quality of being ______," from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -tas (see -ty (2)).
Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]